Looks like a tricky one - (i wrote out my 1st answer before anyone else had posted)

is it possible the rattling is coming from somewhere else and resonating through the steering column? ie - would the rattling happen if you jacked the front of the car up and turned the sterring wheel briskly from side to side, would it still rattle or is it just on rough roads?

Im not saying you are wrong about where the rattling is coming from, but sometimes an annoying rattle may seem to come from one place, is really coming from elsewhere